Conveyor belts on which strippers are used on an industrial scale for transporting overburden, coal, ores, excavated earth and the like, and they circulate endlessly on rollers. Normally, the material for transporting is deposited on one side of the conveyor belt, and falls off the conveyor belt at the turning stations on the other side of the conveyor belt, and the conveyor belt runs back empty on the underside of the conveyor system. However, some of the transported material sometimes becomes caked on the conveyor belt, or becomes stuck to it. It is these caked deposits that the stripper is designed to remove, and for this purpose the stripper is able to be arranged on the flat section or the turning section of the conveyor belt.
However, conveyor belts also have uneven areas and irregularities, for example, the sites where the endless conveyor belt is joined to itself. Strippers must not damage these sites on the conveyor belt under any circumstances. Therefore, the strippers must respond differently to dirt that has stuck to the conveyor belt than they do to irregularities in the conveyor belt itself This distinction usually poses considerable difficulties for purely mechanical stripper systems, which has in turn resulted in the creation of very many different designs therefor.
Patent No. EP 1 529 010 B1 shows a device for stripping soiling from a belt webbing in a conveyor system that has a lamella support disposed on a system carrier so as to be pivotable about a first axis, and is arranged in the turning area of the conveyor belt. A stripping lamella is provided on the lamella support so as to be pivotable about a second axis, the stripping lamella having a first arm and a second arm, which extend diametrically from the second axis. The first arm extends in the direction of the belt webbing and has a stripping edge that lies flush against a belt webbing so as to scrape the surface thereof The second arm of the stripping lamella is provided on the side of the stripping lamella facing away from the belt webbing. The first axis provides a pivot joint for the lamella support relative to the system carrier, wherein a first spring device having a spring element that biases the stripping lamella towards the webbing belt is attached to the pivot joint, so that in a stripping position the stripping lamella lies with the first arm flush against the webbing belt and scrapes soiling from webbing belt. The second axis provides a second pivot point for the stripping lamella relative to the lamella support, wherein a second spring device having a second spring element is attached to the second pivot joint. The spring force of the second spring device is loaded in the opposite direction to the direction of the spring force of the first spring device. The second spring element serves to keep the stripping lamella in the desired stripping position with a scraping attitude relative to the belt webbing. Then, if the stripping lamella encounters a larger obstruction on the belt webbing, the stripping lamella breaks away from the belt webbing due to the two pivot joints that are biased by the two spring elements.
German Patent No. DE 34 02 407 A1 shows another device for stripping soiling from a belt webbing of conveyor systems, attached to the lower, returning section of the belt webbing. This device has a guide that is arranged on a crosspiece so as to be pivotable about a first axis, and a stripping element that is arranged pivotably about a second axis, which stripping element has a first arm facing the belt and a second arm facing away from the belt, and also a spring that is attached to the first axis, which biases a stripping element towards the belt so that the stripping element lies flush against the belt in a stripping position. A guide is also arranged on the second arm of the stripping element and couples the stripping element to the spring.
The drawback associated with these types of stripper is that their construction is complex and complicated due to the large number of individual parts they contain. In order to ensure that the stripping lamella lies perfectly flush against the belt webbing to remove small particles of dirt, but still ensure that the stripping lamella pivots back to avoid larger obstructions, the spring forces of the two spring elements arranged on the two pivot joints must be balanced against each other perfectly, in order to ensure that the belt webbing may be scraped adequately.
Another problem arises after the spring-loaded strippers have been pivoted back, when they are to be returned to their starting positions. On the one hand, this operation must not take too long, on the other hand, the stripping lamella must not strike the belt webbing so fast so that it chops and damages it. In practical terms, this means that only large forces may be used to pivot the strippers back, but the necessary counteracting spring force must not transfer strong impacts to the belt webbing when the strippers are pivoted back into contact with it. However, the corresponding damping devices must slow the return pivot as little as possible. These requirements are fundamentally contradictory.